Effects of UVA and its simultaneous action with blue light on the growth and phototropism of cress leaves under various gravity conditions

Nature Research Centre, Akademijos 2, Vilnius 08412, Lithuania The gravity of the Earth (1g) and phototropic active components of the light spectrum are the stimuli regulating the directional growth of plants. In this study, the role of combined light and gravity effects on plant leaves (Lepidium sativum L.) was tested. Treatment with UVA (370 nm) or UVA combined with blue light together with the gravity in the slow clinostat (clinorotated 3 rpm), or Earth’s gravity (1g), was applied. A custom-built clinostat with LEDs allowed unidirectional illumination of cress leaves. UVA or UVA with blue light was directed laterally at cress leaves for a 3 h exposure. Responses of cotyledons and true leaves, both under 1g and clinorotation conditions, were compared. The obtained data show that UVA (370 nm) suppresses the elongation of cotyledons and true leaves under changed gravity of the Earth. Clinorotation suppresses the growth of cotyledons but not of the true leaves under UVA with blue light. Comparison of leaf phototropism induced by different illuminations under1g and changed gravity conditions revealed that phototropism was induced by clinorotation but suppressed by Earth’s gravity. Phototropic responses of true leaves under clinorotation were stronger than those of cotyledons.